U.S. President Joe Biden tested positive for COVID-19 again on Saturday in what his doctor described as a "rebound" case after taking antiviral medication, the White House said.

Biden "has experienced no re-emergence of symptoms and continues to feel quite well," the White House physician Kevin O'Connor said in a letter released by the White House.

U.S. President Joe Biden. (Getty/Kyodo)

He had been taking the COVID-19 treatment Paxlovid after testing positive on July 21 and experiencing mild symptoms. Some COVID-19 patients treated with the pill are known to show rebound positivity once they cease taking the medication.

"I've got no symptoms but I am going to isolate for the safety of everyone around me. I'm still at work, and will be back on the road soon," Biden said in a tweet.

O'Connor said there is no need to reinitiate treatment for now but he will continue to observe Biden closely.

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